The invention relates generally to power amplifiers and, more particularly, to power measurement and control in a power amplifier.
Power amplifiers (PAs) may be used in a variety of applications to increase the power level of a signal. For example, a power amplifier may be used as the final gain stage in the transmitter of a mobile handset terminal (e.g., a mobile phone). Typically, power measurement and control is required to ensure compliance with regulations imposed on RF emissions and output power. It is also desirable to minimize power consumption by operating at the lowest possible output power levels. The power measurement and control performed at a final test stage of a mobile handset device generally requires a calibration step to program correction coefficients into the mobile handset to compensate for measurement errors. This can be a time consuming and costly process that is generally performed on every mobile handset manufactured by a vendor. In addition, this is a redundant measurement as the manufacturer of the power amplifier also measures the output power of each power amplifier to ensure compliance with specifications.
FIG. 1 is a schematic block diagram of an exemplary GSM (Global System for Mobile communication) transmitter for a mobile handset terminal. A power amplifier module (PAM) 102, coupler 114 and power detector 118 are used to create closed loop power control. Power amplifier module 102 includes a power amplifier integrated circuit 104 and a power controller integrated circuit 106. The power amplifier module 102 may also include RF matching elements 108, filters 110 and RF switches 112. Power amplifier module 102 is used to adjust the input power level of an RF signal to a required power level and deliver the RF signal with an output power level to an antenna 116 load.
To control the output power level of the RF signal, a coupler 114 samples the output power level of the signal and sends the sample to a power detector 118. The power detector 118 may be, for example, a logarithmic amplifier. The sampled output power is measured by the power detector 118 and the measured power is delivered to the power controller 106. Power controller 106 compares the measured power to a power set voltage 120 (i.e., a voltage level corresponding to the desired power level) input to the power controller 106. The manufacturer of the mobile handset terminal must provide a power set voltage 120 that has been corrected (or calibrated) for error caused by various factors such as temperature variation, detector variation with power level and filter/coupler loss variations. A manufacturer may, for example, apply an algorithm to adjust the power set voltage 120 for the average non-linearity of the detector. These calibration corrections are then stored in memory in the mobile handset terminal.
The power controller 106 then controls the power amplifier 104 based on the comparison of the measured output power to the power set voltage so that the output power level of the power amplifier matches the desired power level. Generally, a manufacturer of a mobile handset will measure the power of each hand set after assembly and program the correction factors into the handset memory. As mentioned above, this can be a costly and time-consuming process. In addition, the process is redundant since each PAM 102 itself must be measured against power specifications.
In accordance with one aspect of the invention, a power amplifier module includes an input for receiving a signal having an input power level, at least one power amplifier to increase the input power level of the signal to an output power level, a power detector to measure the output power level, a power controller for comparing the output power level to a target power level and producing a control signal for the power amplifier based on the comparison and a power calibrator for determining a correction based on a set of factors. A power set interface may be coupled to the power controller to provide the target power level. The power amplifier module may further include a power sampling element for sampling a portion of the output power level and delivering the sampled output power to the power detector.
In one embodiment, the power calibrator adjusts the target power level based on the correction. Alternatively, the power calibrator may adjust the measured output power level provided by the power detector or the control signal produced by the power controller.
In another embodiment, the power detector is a logarithmic amplifier. The power calibrator may include a set of laser trimmed resistors. In a further embodiment, the power amplifier module further includes a set of calibration pins coupled to the power calibrator for receiving a voltage to program at least one of the set of factors. Alternatively, the set of factors may be digitally programmable. The power set interface may be a digital or analog interface. In yet another embodiment, the power amplifier, the power detector, the power controller and the power calibrator are implemented on a single semiconductor die. The power amplifier module may further include RF matching elements or RF switches. The power set interface may provide a controlled power burst for GSM and EDGE signals.
In accordance with another aspect of the invention, a power amplifier module includes an input for receiving a signal with an input power level, at least one power amplifier for increasing the input power level of the signal to an output power level and means for measuring the output power level. The power amplifier module also includes means for comparing the measured output power level to a target power level and producing a control signal and means for adjusting at least one of the measured output power level, the target power level and the control signal using a correction based on a set of factors.
In one embodiment, the power amplifier module further includes a power set interface for providing the target power level. In another embodiment, the power amplifier module further includes means for sampling the output power level from the at least one power amplifier. A set of calibration pins may be coupled to the means for adjusting to receive a voltage to program at least one of the set of factors. Alternatively, the set of factors may be digitally programmable. The power set interface may be a digital or analog interface.
In accordance with another aspect of the invention, a power amplifier module includes an input for receiving a signal having an input power level, at least one power amplifier to increase the input power level of the signal to an output power level. The power amplifier module further includes a power calibration and control module for measuring the output power level and correcting the output power level measurement based on a set of factors. The power calibration and control module may also control the at least one power amplifier to produce an output power level equivalent to a target power level.
In one embodiment, the power amplifier module further includes a power set interface coupled to the power calibration and control module for providing the target power level. The power set interface may be a digital interface or an analog interface. In another embodiment, the power amplifier module includes at least one power sampling element coupled to the at least one power amplifier and the power detector for sampling a portion of the output power level of the signal and delivering the sampled output power level to the power calibration and control module.